The 4th International Symposium on Mine Safety Science and Engineering (ISMSSE2018)

387 / 2018-09-13 19:29:05

Study on the Ultrasonic Propagation Characteristics of Coal Samples Containing Hole Defects

Coal samples; hole defects; propagation characteristics; attenuation coefficients

Gas of Coal Mine & Coal and Gas Outburst > Coal and gas outburst

In this study, a physical model simulation method was proposed to examine coal samples containing holes formed in the coal body due to geological processes. The coal samples from Zhao Gu No. 2 Coal Mine was taken as the study object. The propagation characteristics of the ultrasonic waves in the coal samples with hole defects were studied using theoretical analyses, laboratory testing, and numerical simulations. The results of the study revealed the following: (1) The inclination angles of the coal samples ranged from 0 to 90°. It was observed that with the increases in the inclination angles, the attenuation coefficients displayed linearly increasing trends, which were completely opposite to the change trends of the transmission coefficients; (2) The longitudinal wave velocities and first wave amplitudes had decreased following the drilling of the coal samples, and the decrease rates of the first wave amplitudes were found to be larger than those of the longitudinal wave velocities. In other words, the influences of the holes with different inclination angles in the coal samples on the dynamic characteristic parameters of the ultrasonic waves (amplitude and attenuation coefficients) were much greater than the influences on the kinematic characteristics (velocity); (3)When the inclination angles of the holes were 30°, and the frequency was 50 kHz, the detectable hole diameter range was within 0 to 54.6 mm when the ultrasonic waves penetrated through the coal samples containing circular holes; (4) When the inclination angles of holes were 30°, and the hole diameters were approximately 10 mm, the attenuation coefficients were observed to increase with the increased frequencies of the ultrasonic waves. The results of the current study have certain potential reference values for the detection of mining goafs or abandoned mine laneways using seismic or low-frequency waves.